Joe E. Maskasky, "Epitaxial Selective Site Sensitization of Tabular Grain Emulsions", Journal of Imaging Science, Vol. 32, No. 4, July/August 1988, and Maskasky U.S. Pat. No. 4,435,501 report investigations of the epitaxial deposition of silver halide (typically high chloride) salts on high bromide tabular grains. In most of the tabular grain emulsions, the epitaxy is present at a number of sites on the host tabular grains. In most of these emulsions the epitaxy lies at multiple sites along the edges of the tabular grains, ranging from an almost continuous edge band to sites confined to the corners of the grains. Maskasky in FIG. 10 (article) and FIG. 21 (patent) discloses single site epitaxy confined to the center of the host tabular grains. Single site deposition was accomplished by forming the central portion of the host tabular grains of silver bromide and growing the laterally surrounding region to contain 12 mole percent iodide, based on silver.
Levy U.S. Pat. No. 5,612,177 is an improvement on Maskasky that shows a performance advantage for growing the silver salt epitaxy as terraces extending inwardly from the edges of host high bromide {111} tabular grains. Single site epitaxy is not disclosed.
Illustrations of silver halide epitaxy at the corners of high bromide ultrathin {111} tabular grains are provided by Daubendiek et al U.S. Pat. Nos. 5,494,789, 5,503,971 and 5,576,168, and Deaton et al U.S. Pat. No. 5,582,965.
Eshelman et al U.S. Pat. No. 5,612,175 illustrates silver halide epitaxy on high bromide {111} tabular grains, with the epitaxy being limited to less than 5 percent of total silver. Eshelman et al U.S. Pat. Nos. 5,612,176 and 5,614,359 illustrate silver halide epitaxy on high bromide {111} tabular grains that have an average ECD of greater than 10 .mu.m.